Method, device and system for the temporary marking of objects

ABSTRACT

The invention concerns a method, a device and a system for applying a detectable temporary mark of predefined life time of minutes to hours onto an object ( 0 ). The invention also concerns a coating composition comprising a short-lived radioactive isotope and the use of a short-lived radioactive isotope as a temporary marking. The temporary mark is applied to the object (O) by the means of a coating composition ( 3 ) comprising a low level of a short-lived radionuclide, generated in situ from a longer-lived precursor nucleus. The marking device comprises a radionuclide generator ( 1 ), a reservoir ( 2 ) for the in situ preparing the radioactively marked printing ink, and an ink-jet or alike printing or spraying head ( 8 ), preferably of the dropon-demand type. The marking is preferably detected and identified by a gamma-radiation counter. The invention claims also a system for the temporary marking of an object (O) with a radioactive isotope of predefined life time of minutes to hours, in view of performing an operation on the marked object (O) at a later point in time.

FIELD OF INVENTION

The invention is in the field of marking and identifying objects. It isin particular about a method, a device and a system for applying aninvisible mark which is lasting and detectable only during a determinedtime.

STATE OF THE ART

The marking of objects for identification and authentication purposes isknown in the art, and a large variety of physical effects have beenexploited to this aim, such as the marking of documents or goods withspecial inks, containing e.g. one or several UV-luminescent compounds.Such markings remain invisible to the unaided eye and can only beevidenced by irradiation with appropriate UV-light. The said kind ofmarking has also the property of being permanent, lasting over the wholelife of the correspondingly marked banknote, passport, credit card,branded good, etc.

In some cases, a temporary marking of documents or goods is required,e.g. for distinction purposes in a process chain, wherein a marking,indicating a distinction, is applied to determined objects in a firstpart of the process, and an action, corresponding to the saiddistinction, is performed on the marked objects in a second part of theprocess, whereby the said second part of the process is performed at alater point in time at another location. The marking, having the onlyaim to indicate that the said action is to be performed on the markedobject, must in general be removed after the action has been performed.

In the easiest case, the said marking may be a simple color mark or alabel, and the said removal of the marking may be performed by a simplecleaning operation. There are, however, more delicate applications,where the marking should remain invisible, where it should be read-ableby a machine, and where it has to disappear of its own after adetermined time, due to the impossibility of removing it by a cleaningoperation.

The stated technical problem requires to all evidence some sort ofintrinsic timing mechanism to be put in place. Chemical timing, takingprofit of a suitable chemical reaction under the influence oftemperature, light, oxygen or humidity, is not sufficiently reliable,because chemical reaction rates are very dependent on temperature and onpossible catalytic influences of the substrate to which the marking wasapplied. A similar reasoning holds for a timing based on the physicalevaporation or diffusion of a marker compound. Evaporation and diffusionprocesses are, like chemical reactions, very environment- andtemperature-dependent. Furthermore, because the marker compound does notreally disappear in these processes, a cross-contamination of unmarkedobjects through their contact with a marked object might result.

An invisible marking which is detectable by instrumental means and whichfades away in time by its own in a foreseeable manner, has not beendisclosed up to now.

Although some applications of radioactive isotopes for marking purposeshave been disclosed in the prior art, such as in U.S. Pat. No.3,805,067, “Method of secretly marking a surface employing fissionproducts”, in U.S. Pat. No. 3,959,630, “Identity card having radioactiveisotope of short half-life”, and in WO 02/00440 A2, none of thesedisclosures has addressed the above stated technical problem. The citeddocuments describe a tedious and time-consuming implantation ofradioactive fission products, within the material.

SUMMARY OF THE INVENTION

The only absolute and environment-influence independent intrinsic timingmechanisms known in nature are the “atomic decay clocks” of radioactiveisotopes. The stated technical problem is thus solved according to theinvention by a marking of the said object with a short-lived radioactiveisotope.

According to the present invention the method of temporary marking anobject comprises the step of applying a coating composition whichcomprises an appropriate, short-lived radioactive isotope. In thecontext of the invention the term “short-lived” is defined as ahalf-life time of the radioactive isotope which ranges between a minuteand a day, preferably between a plurality of minutes and a plurality ofhours. The radioactive isotope (radionuclide) is preferably chosen tohave a half-life which is comparable to the time delay required in thesaid process between the marking operation and the process action to betaken, especially the identification step, i.e. of the order of aplurality of minutes to a plurality of hours.

The coating composition may further comprise a binder, such as to ensurefixation of the radioisotope on the marked object, in order to avoid anyloss of the marking, or cross-contamination through the contact of amarked with unmarked objects. Said binder may noteworthy be present inextremely tiny amounts, such as to avoid any visible impact of themarking.

The said isotope is furthermore chosen such as to result in an easydetection of its presence at a certain distance, preferably by the wayof a gamma-radiation of sufficient energy which is emitted during itsradioactive decay. Isotopes having exclusively particle emissions, suchas α- or β⁻-radiation, which are strongly absorbed by air or by anyother material, render difficult a reliable and sensitive detectionunder all practical circumstances. Isotopes emitting β⁺-radiation aredetectable, however, through the 511 keV electron-positron anihilationγ-radiation.

Half-life time and applied quantity of the said isotope ate chosen suchas to result in a reliable detection under the required operatingconditions, using state-of-the-art detection equipment. Reliabledetection means that the detector signal obtained from the marking ispreferably at least five standard deviations above background.

Radioactive decay events do noteworthy obey POISSON-type statistics,i.e. the standard deviation of a measured number of events is equal tothe square root of the said number of events. Let B=the background(number of counts measured in an appropriate time interval Δt) in theabsence of the marking, and S=the signal (number of counts measured inthe same time interval Δt) in the presence of the marking, then thestandard deviation c(S)=(S)^(1/2). The condition for reliable detection,such as stated above, translates then into S>=5*(S)^(1/2)+B. Forexample, taking a background B of 10, a measured S of 50 will fulfillthe set condition of a reliable detection.

From the stated above it is easily inferred that very low quantities ofapplied radioactive isotope will suffice to the marking purpose. Thisminimum of required radioactivity will have safely decayed below thebackground level after as few as three half-life times. The requiredactivities for the marking are in all cases very much lower than thoseemployed in medical radiographic applications.

The radioactive isotope is preferably chosen such as to allow itssolubilization in the coating composition. The possibility to solubilizethe isotope is hereby not only a function of the nature of the chemicalspecies containing it—at the required low concentration levelseverything is soluble—but depends principally on the chemical nature ofthe radioactive precursor material from which the isotope is drawn.

Short-lived radioactive isotopes can noteworthy only be handled in apractical application, if they can be generated in situ as decay(daughter) products of a longer lived radioactive parent isotope. Insuch a case, the short-lived isotope is in a secular equilibrium (i.e.where all concentration of the decay chain elements are at steady state)with its radioactive precursor, adopting the precursor's numericalactivity and half-live time. As soon as the daughter isotope isseparated from its parent, it decays according to its own, shorter livetime.

This implies that the parent isotope must exist in a chemical form whichallows an easy separation of the generated daughter product from itsgenerating parent. Only few isotopes are known to fulfill all of theherein required conditions, which are noteworthy: i) to show ashort-lived decay with emission of γ-radiation; ii) to have asufficiently long-lived parent isotope; and iii) to have chemicalproperties which allow their easy separation from their parent isotope.

One of these isotopes, which has been extensively studied and which isused in medical applications, is 99m-Technetium. 99m-Tc is a γ-emitterwith an energy of 142.68 keV, having a half life of 6.01 hours. Thisisotope is a metastable energy level in the β-decay of 99-Molybdenum to99-Technetium. 99-Mo in turn has a half life time of 66 hours (2.75days). 99-Mo is a fission product of 235-Uranium in nuclear reactors andis currently extracted from nuclear fuel irradiated in speciallydesigned reactors. It can also be produced by high-flux neutronirradiation of a 98-Molybdenum target.

99m-Technetium generators, containing the 99-Mo precursor isotope in thechemical form of molybdate ions attached to an ion exchanger, to a gelor to a similar chromatographic support, are commercially available fromradiopharmaceutical companies.

The 99m-Tc can be ‘milked’ from these generators by simple elution, inintervals corresponding to its replenishing through the decay of theparent 99-Mo. The useful life time of a 99m-Tc generator is about 5half-life periods of the 99m-Mo precursor, i.e. about 2 weeks. Afterthis time the generator has to be exchanged by a new one.

According to the present invention, the 99m-Tc obtained from a generatorof this type is in situ mixed into the printing liquid in a controlledway, such as to obtain a liquid of controlled, standardizedradioactivity.

The marking of an object in question is effectuated by applying adetermined quantity of the said printing liquid to its surface. This canbe done by any known method in the art; preferably by ink-jet printingor spraying methods of the drop-on-demand type, as these methods have noneed for external (radioactive) ink recycling. The printing head's inkflux actuators can hereby be of the electromechanical or of thepiezoelectric type; the ink is preferably internally cycled through theprinting head, in order to keep its radioactivity level constant and toprovide for the needed pressure gradient during the printing or markingoperation.

The ‘printing’ operation can furthermore be performed either as a simplemarking, or, alternatively, in the form of indicia, which might be readby corresponding radiation-sensitive area detection equipment within thelife time of the used radioisotope. The printing or marking operationmay be triggered upon receipt of a corresponding signal, preferably anelectric signal.

The quantities of radioactive isotope which need to be applied for themarking according to the present invention are so small, that notoxicological issues are of concern, other than the direct radiationeffects; in fact, the number of isotopic atoms deposited in the markingis far below the detection limit of most conventional analyticalinstruments, as well as far below the established chemical toxicitylevels.

The total number of radioactive atoms N required in the marking can becalculated from the half-life t_(1/2) of the isotope and the desiredinitial absolute decay rate I₀ according to the formulaN=1.44*I₀*t_(1/2); the preferred absolute initial decay rate I₀ is lowerthan 1000 Becquerel (decays per second). Using an isotope with ahalf-life of 10 minutes, less than 1 Million atoms are required,corresponding to less than 1.6*10⁻¹⁸ mole.

The marking method according to the present invention is feasible withany short-lived radioactive isotope, which is a direct or an indirectdaughter of a long-lived radioactive parent isotope, and for which amethod of chemical separation is known. The following radioisotopes cannoteworthy be used for alternative embodiments of the marking device:

-   60-Fe parent (half-life of 1.5 million years)-   generates 60m-Co (half-life of 10.5 minutes) as the marker isotope,    producing 60-Co (half-life of 5.27 years), which decays to the    stable 60-Ni at a rate below the radioactive background level.-   90-Sr parent (half-life of 28.79 years)-   generates 90m-Y (half-life of 3.19 h) as the marker isotope,    producing 90-Y (half-life of 64 h) which decays to the stable 90-Zr    at a rate of 5% of the original activity level.-   103-Ru parent (half-life of 39.26 days)-   generates 103m-Rh (half-life of 56 minutes) as the marker isotope,    producing the stable 103-Rh.-   106-Ru parent (half-life of 373.6 days)-   generates 106m-Rh (half-life of 131 minutes) as the marker isotope,    producing 106-Rh (half-life of 29.8 sec) which decays to the stable    106-Pd immediately.-   137-Cs parent (half-life of 30 years)-   generates 137m-Ba (half-life of 2.55 minutes) as the marker isotope,    producing the stable 137-Ba.-   144-Ce parent (half-life of 285 days)-   generates 144m-Pr (half-life of 7.2 minutes) as the marker isotope,    producing 144-Pr (half-life of 17.28 minutes) which decays to the    stable 144-Nd.

Another source of short-lived radioactivity which can be used in thecontext of the present invention, is 232-Thorium (half-life of 1.4*10¹⁰years), or, preferably, its first direct daughter isotope 228-Radium(half-life of 5.7 years). FIG. 1 a shows the decay scheme of the232-Thorium radioactive family. The effective marker isotope is 212-Lead(212-Pb, half-life of 10.6 hours), which is in a secular equilibriumwith its longer lived radioactive parents. A member in this equilibriumchain is the gaseous 220-Radon (Thoron, half-life of 55.6 sec), whichcan be used to draw the radioactivity via an air stream from the thoriumor radium source, respectively, and to transfer it into the coatingcomposition, where the 220-Rn decays to 212-Pb. The so producedradioactivity of the coating composition, due to 212-Pb, will havecompletely disappeared after about one week from switching off thedevice.

Still another source of suitable radioactivity is 235-Uranium (half-lifeof 7.0*108 years), or one of its daughter nuclei, preferably227-Actinium (half-life of 21.77 years), which can be used as agenerator for the marking isotope 211-Lead (211-Pb, with a half-life of36.1 minutes). FIG. 1 b shows the decay scheme of the 235-Uraniumradioactive family. A member of the secular equilibrium chain, linkingthe 211-Pb to its longer lived radioactive parents, is the gaseous219-Radon (half-life of 3.9 seconds). The Radon can be drawn from thegenerator by an air stream and introduced into the coating composition,where it decays to 211-Pb. The final product of the 211-Pb decay is thestable isotope 207-Pb. The so produced radioactivity of the coatingcomposition, due to 211-Pb, will have completely disappeared after about6 hours from switching off the device.

The isotope generator part is handled as an integrated, modular unit,purchased as such from an isotope facility; this means that nomanipulations are performed on it at the user level, except using itaccording to its specifications. 99m-Tc generators need to be exchangedevery two weeks; whereas a 228-Radium based 212-Pb generator will lastfor about 30 years, and an 227-Actinium based 211-Pb generator for about100 years.

The equipment used to detect the marking of the invention is preferablya γ-detector of the scintillator- or of the semiconductor-type. Inscintillator-detectors, a γ-quantum produced in the radioactive decay ofa marker isotope is absorbed in a heavy-atom containing, opticallytransparent solid (e.g. a crystal of a material like NaI:Tl, CsI:Tl, BGO(bismuth germanate), CWO (cadmium tungstate), or PWO (lead tungstate)),producing a plurality of low-energy photons in the UV-, visible-, orNIR-spectral range. The number of photons produced is hereby more orless proportional to the energy of the original γ-quantum. The saidphotons are subsequently detected by a photomultiplyer tube, operatedsuch as to discriminate the γ-rays according to their relative energies.The γ-rays falling into a preset energy window are taken as originatingfrom the marker isotope and counted.

An interesting variant of scintillator detectors, such as described e.g.in U.S. Pat. No. 4,788,436, uses correspondingly doped optical fibers asthe active absorber medium for the γ-rays. The generated photons travel,in both senses, down the fiber in which they were generated, torespective photomultipliers disposed at the ends of the fiber, where thecorresponding light pulses are discriminated and counted. Optical fibersnoteworthy allow to give in an easy way an almost arbitrary shape to thedetecting interface, which can in consequence be made in the form of agate or of any other convenient construction. Radiation-sensing opticalfibers are commercially available from a number of suppliers, e.g. fromMitsubishi Electric.

Still another variant of γ-ray detectors is based on a direct chargecarrier generation by the absorption of the γ-ray in an appropriatesemiconductor material, such as Silicon, Germanium, CdZnTe₂, and others.In a further variant, a silicon photodiode is used in conjunction with ascintillator crystal. All these types of γ-ray detectors are known tothe skilled in the art and commercially available from various sources,e.g. from Mitsubishi Electric; they need not, thus, to be furtherdescribed here.

The invention comprises as well a system for temporarily marking anobject and detecting said marking later in time for performing aspecific action on said marked object. The system according to theinvention comprises at least one device for temporary marking an objectand at least one detecting device for detecting the presence of atemporary marking on an object. The marking device for applying thetemporary marking comprises a short-lived-radionuclide generator, afirst reservoir of a printing liquid, a radiation, monitor, a controlunit and a printing or marking head. The marking device is activatedupon receipt of a signal, e.g. an electric signal. The detecting deviceis capable of detecting of gamma-radiation and producing a signal,preferably an electric signal, upon detection of the said temporarymarking. Said signal, e.g. an electric signal, may then be used toperform a specific action upon said marked object, such as taking it outof a stream of similar objects.

Preferably the marking device and the detecting device are locallyseparated from each other. In a preferred embodiment the marking devicefurther comprises a splitting valve and/or a pump. In a furtherembodiment the marking device may comprise a second reservoir forstoring a coating composition, preferably a printing ink, which does notcontain any short-lived radioactive isotopes, i.e. which is free of theisotopes. This reservoir is used to refill the first reservoir andmaintain an almost constant level of liquid within the first reservoir.

The system may comprise, if needed, a plurality of independent markingdevices; it may also comprise, if needed, a plurality of independentdetection devices. The marking, respectively detection devices mayfurthermore be either of the same or of different types, as to the usedmarker radionuclide and to the used detection hardware A marking devicemay also be associated with an external radiation detector in order toverify if the marking has been correctly applied.

Another aspect of the invention is a coating composition, preferably anink-jet printing ink. The coating composition is characterized in thatit comprises at least one short-lived radioactive isotope.

The coating composition and there especially the ink-jet printing inkcomprises as a main component a liquid which can be a simple solvent,such as water, ethyl alcohol, isopropanol, mixtures thereof, or anyother solvent or solvent mixture with easy evaporation. Preferably,however, the coating composition comprises minor amounts, i.e. less than1% by weight, of additives, destined i) to enhance the wettingproperties of the coating composition on the various substrates, ii) tofix the marking on the substrate, and iii) to prevent a foaming of thecoating composition in the marking device. The additives for i) areselected from the classes of anionic, cationic or neutral surfactants;the additives for ii) are selected from the classes of water-soluble andsolvent-soluble, non-crosslinkable binders, such as starch, polyvinylalcohol, ethyl cellulose, acetyl cellulose, polyacrylic derivatives andthe like. The amount of binder incorporated within the ink ranges atmaximum up to 5 wt % referred to the total weight of the coatingcomposition.

Preferably, the binder is used in a concentration of less than 2 wt %and even more preferred in a concentration of less than 0.1% by weight.;the additives for iii) are selected from the class of antifoamingagents. Depending on the application, further additives may be provided,such as bactericides, electrolytes, and the like.

Radioactive isotope being incorporated within the coating compositionare identical to the ones describe before.

Still other embodiments of the invention, using other radioisotopesand/or other detecting equipment and/or other device lay-outs, can beeasily conceived by the skilled in the art based on the disclosure givenherein. The invention will now be outlined further with the help of thedrawings and of an exemplary embodiment.

FIG. 1 a) shows the natural 232-Th decay chain

-   -   b) shows the natural '235-U/227-Ac decay chain

FIG. 2 schematically shows an embodiment using a 99m-Tc generator

FIG. 3 schematically shows an embodiment using a 212-Pb generator

FIG. 4 schematically shows an application of a marking system accordingto the invention, comprising a marking device and a spatially separatedautomated detection device (gate).

EXAMPLES

According to a first embodiment of a marking device for marking anobject (O) according to the present invention and with reference to thescheme of FIG. 2, a shielded 99m-Tc generator (1) is employed as thesource of the radioactive isotope. The marking device comprises further,in addition to the said source of radioactive isotope, a reservoir (2)containing a colorless printing liquid (3), a circulating pump (4), asplitting valve (5), a radiation monitor (6), a control unit (processor)(7), as well as a printing or marking head (8) with its correspondingcontrol electronics (9). The printing liquid (3) in the reservoir (2),which is typically an ink-jet ink base without colorants nor pigments,is continuously circulated by the said circulating pump (4). A part ofsaid printing liquid is deviated, via said splitting valve (5), throughthe said 99m-Tc generator (1), where it is loaded with 99m-Tc activity,before flowing back to the reservoir (2). The total 99m-Tc activity ofthe printing liquid in the reservoir is monitored by said radiationmonitor (6) and said control unit (7), which is in turn enabled toactuate said splitting valve (5) so that the resulting 99m-Tc activityof the printing liquid (3) remains at a predetermined level. The wholedevice is contained within an appropriate radiation shielding (10), suchthat no radiation hazard is created for the operating personnel. Thetotal volume of radioactive ink (3) in the device is advantageously keptsmall, and a second, non-radioactive ink reservoir (11) may be provided,for replenishing the ink reservoir (2) with non-radioactive fluid (12)upon need, by the means of a dosing pump (13) and a level sensor (14)which are both controlled by the said processor (7).

If the marking device is switched off, the 99m-Tc activity of theprinting fluid decays according to the half-life of the 99m-Tc isotopeof 6 hours, i.e. to about 12.5% of its initial value after one day, to1.5% after two days, and to 0.2% after three days of waiting. This meansthat after a waiting period of some days, no significant radioactivityis any longer present in the equipment, except in the shielded 99m-Tcgenerator, such that the equipment can be freely serviced or repaired.

After the decay of the 99m-Tc in the marking, the resulting 99-Tcisotope is radioactive as well, decaying to the stable 99-Ru with ahalf-life of 210'000 years. However, at the employed quantities, thislong-term activity is absolutely harmless, and its contribution isactually negligible compared with the background radioactivity presentin all living being, which is due to the naturally occurring radioactiveisotope 40-K (0.0117% of the natural potassium; half life of 1.28*10⁹years; β⁻-, β⁺-, and γ-emitter); potassium being a necessary constituentof life on earth.

According to a second embodiment and with reference to the scheme ofFIG. 3, the marking device for marking an object (O) according to thepresent invention comprises a 228-Radium based 212-Pb generator as thesource of the radioactive marking isotope. The 228-Ra is contained in adry and shielded generator package (1), where it is in a secularequilibrium with its daughter nuclei, noteworthy with the gaseous220-Radon (Thoron, half-life of 55.6 sec). The device comprises furthera reservoir (2) containing a colorless printing liquid (3), an air pump(4), a circulating pump (5), a radiation monitor (6), a control unit(processor) (7), as well as a printing or marking head (8) with itscorresponding control electronics (9). The printing liquid (3) in thereservoir (2), which is typically an ink-jet ink base without colorantsnor pigments, is continuously circulated through the printing head (8)by the pump (5). Controlled by the processor (7), air containing220-Radon is drawn from the generator package by the means of the airpump (4), and bubbled through the liquid (3) with the help of a porousfritted glass interface (F). The total “220-Rn and daughters” activityof the printing liquid (3) in the reservoir (2) is monitored with theradiation monitor (6) and the processor (7), which is enabled to act onthe air pump (4) such that the resulting, mainly 212-Pb originatedradioactivity of the printing liquid stays at a predetermined level. Thewhole device is contained in an appropriate radiation shielding (10),such that no radiation hazard is created for the operating personnel.The total volume of radioactive ink (3) in the device is advantageouslykept small, and a second, non-radioactive ink reservoir (11) may beprovided, for replenishing the ink reservoir (2) with non-radioactivefluid (12) upon need, by the means of a dosing pump (13) and a levelsensor (14) which are both controlled by the said processor (7).

The printing liquid essentially contains only short-lived isotopes,212-Pb having the longest half-life (10.6 hours) of all of them. Afterswitching off the device, the activity of the marking liquid drops afterone day to 21%, after two days to 4.3%, and after three days to 0.9% ofits original value. This means that after a waiting period of about aweek, no significant radioactivity is any longer present in theequipment, except in the shielded generator part, such that theequipment can be freely serviced or repaired. The final product of the212-Pb decay is stable 208-Pb.

An marking & detecting system according to the invention, with referenceto the scheme of FIG. 4, comprising a plurality of marking stations anda single detection station is embodied as follows:

A locket hall of a post office comprises a series of lockets (L). Amarking device (D) according to the invention (e.g. FIG. 2) is locatedat each locket (L), at the point where objects (O) are accepted forweighing and shipping. During the weighing operation, and triggered byan electric signal, an invisible radioactive and fast-drying ink-jetmark may be applied to the lower part of the object (O). The request tomark a determined object (O) may hereby either be given manually, or itmay be automatically generated as a consequence of the fulfillment ofpredetermined conditions such as the destination of the object.Immediately after the marking operation, the object passes over aγ-counter (C), connected to the marking device (D). If the applied markis detected by the γ-counter (C), the marking operation is assumed to besuccessfully concluded, and the object (O) is sent via a conveyor belt(B) to a central collection point (P). If no marking is detected bycounter (C) for an presumably marked object, a failure alert is given,allowing the operating personnel of the locket to take the appropriatemeasures.

At the central collection point (P), the objects pass a gate (G),comprising a scintillator detector and corresponding processingelectronics for detecting, discriminating and counting γ-radiation. Thegate (G) is further connected to a mechanical actuator (A) for deviatingobjects (O) from the main track (M) to a secondary track (S), ifrequired. Upon detection of γ-radiation corresponding to a marking on anobject (O), the mechanical actuator is set such as to deviate the markedobject (O) from the mainstream to the secondary track (S). The in thisway separated objects are conveyed to an examination station (notshown), where they are subject to X-ray scanning and/or otherappropriate detecting operations, and where they can also be manuallyexamined, if needed, before giving them their final destination. Theunmarked objects, in turn, are passed straight on via the main track(M), to be charged on board of a transportation vehicle.

The skilled in the art may conceive, based on the disclosure madeherein, many other variants of the marking method, the marking deviceand the marking & detection system.

1. A method for temporary marking an object (O) in a process chain, themethod comprising the step of applying a coating composition (3) to theobject (O) by a marking device, the said coating composition (3)comprising a short-lived radioactive isotope, wherein said short-livedradioactive isotope is generated in situ from a longer-lived radioactiveprecursor isotope and added to said coating composition (3) in saidmarking device.
 2. Method according to claim 1, characterized in thatsaid short-lived radioactive isotope has a half-life time comprisedbetween a minute and a day.
 3. Method according to claim 1 or 2,characterized in that said short-lived radioactive isotope is agamma-radiation emitter or a β(+)-emitter.
 4. Method according to one ofclaims 1 to 3, characterized in that the short-lived radioactive isotopeis selected from the group comprising 99m-Tc, 60m-Co, 90m-Y, 103m-Rh,106m-Rh, 137m-Ba, 144m-Pr, 144-Pr, 212-Pb, and 211-Pb.
 5. Methodaccording to one of the preceding claims, characterized in that thecoating composition (3) is applied to said object (O) by ink-jetprinting or by a spraying operation.
 6. Method according to claim 5,characterized in that said ink-jet printing or spraying is of thedrop-on-demand type.
 7. Method according to one of the preceding claims,characterized in that said coating composition (3) contains at least onebinder.
 8. Method according to one of the preceding claims,characterized in that the application of the coating composition (3) isperformed upon receipt of a particular signal, preferably an electricsignal, by said marking device.
 9. Device suitable for temporary markingan object (O) in a process chain, said device comprising a short-livedradionuclide generator (1), a first reservoir (2) of a printing liquid,a splitting valve (5), a radiation monitor (6), a control unit (7) and aprinting or marking head (8).
 10. Device according to claim 9, whereinsaid radionuclide generator (1) generates a gamma-emitting orβ(+)-emitting radioactive isotope, said radioactive isotope having ahalf-life time comprised between a minute and a day.
 11. Deviceaccording to claim 10, wherein said radionuclide generator (1) generatesa gamma-emitting short-lived radioactive isotope, which is preferablyselected from the group comprising 99m-Tc, 60m-Co, 90m-Y, 103m-Rh,106m-Rh, 137m-Ba, 144m-Pr, 144-Pr, 212-Pb, and 211-Pb.
 12. Deviceaccording to one of the claims 9 to 11, wherein said printing or markinghead (8) is an ink-jet printing head, preferably a drop-on-demandink-jet printing head.
 13. Device according to one of the claims 9 to12, wherein said device comprises further a second reservoir (11),containing printing liquid, and a dosing pump (13), the printing liquidbeing free of radioactive isotopes.
 14. A system for temporary markingan object (O) in a process chain, said system comprising a) at least onedevice for temporary marking an object (O), preferably a deviceaccording to one of the claims 9 to 13; and b) at least one detectingdevice for detecting the presence of the temporary marking on an object(O), wherein the device for applying the temporary marking comprises ashort-lived radionuclide generator (1), a first reservoir (2) of aprinting liquid, a splitting valve (5), a radiation monitor (6), acontrol unit (7) and a printing or marking head (8), wherein the deviceis activated upon receipt of a signal, preferably an electric signal,and wherein the detecting device is capable of detectinggamma-radiation, and producing a signal, preferably an electric signal,upon detection of said temporary marking.
 15. A method for temporarymarking and identifying an object (O), the method comprising the stepsof applying a coating composition (3) to the object (O), by a markingdevice, wherein the coating composition (3) comprises a short-livedradioactive isotope; and identifying the temporary marking by detectinggamma-radiation emitted by the short-lived radioactive isotope; whereinsaid short-lived radioactive isotope is generated in situ from alonger-lived radioactive precursor isotope and added to said coatingcomposition (3) in said marking device.
 16. Use of a short-livedradioactive isotope in an ink or coating composition for temporarilymarking and identifying an object (O) in a process chain, wherein saidshort-lived radioactive isotope is generated in situ from a longer-livedradioactive precursor isotope and added to said coating composition (3)in said marking device.